1. Technical Field
The present disclosure relates to a hybrid vehicle having an engine that is connected to a power split mechanism, a generator, an electric motor, and also a stepped transmission that is arranged between the electric motor and an axle.
2. Description of Related Art
Conventionally, there is known a hybrid vehicle having an engine that is connected to a power split mechanism, a generator, an electric motor, and also a stepped transmission that is arranged between the electric motor and an axle (e.g., Japanese Patent Application Publication No. 2014-082855 (JP 2014-082855 A) and the like). In this hybrid vehicle, a changeover among gear stages of the stepped transmission is made in accordance with an accelerator opening degree for a vehicle speed.
By the way, the electric motor and the generator (which will not be distinguished from each other and refereed to hereinafter as “a rotating electrical machine”) that are mounted in this hybrid vehicle generate heat as a result of the driving thereof. In the conventional hybrid vehicle, when the rotating electrical machine reaches an excessively high temperature due to this heat, the output of the vehicle is limited to prevent the temperature of the rotating electrical machine from further rising. This limitation on the output of the vehicle leads to a deterioration in driveability.
It should be noted herein that Japanese Patent Application Publication No. 2013-139258 (JP 2013-139258 A) discloses the following art. That is, when the temperature of an electric motor is outside a predetermined range, a first shift mechanism that transmits a power from the electric motor and a power from an internal combustion engine toward driving wheels is neutralized. During this neutralization, the rotational speed of the electric motor is lowered, or the electric motor is stopped from rotating. Thus, the temperature of the electric motor is lowered. According to this art, the electric motor can be prevented from reaching an excessively high temperature, but the power from the electric motor is temporarily not transmitted to the driving wheels. Therefore, the output of the entire vehicle decreases.
Besides, Japanese Patent Application Publication No. 2005-170143 (JP 2005-170143 A) discloses the following art. That is, when the remaining capacity of a battery decreases, a downshift of a stepped transmission is made to increase the torque generated by a generator. However, a rise in the temperature of a rotating electrical machine is not taken into account at all in this Japanese Patent Application Publication No. 2005-170143 (JP 2005-170143 A). Besides, a vehicle of Japanese Patent Application Publication No. 2005-170143 (JP 2005-170143 A) does not have a power split mechanism, so the art of Japanese Patent Application Publication No. 2005-170143 (JP 2005-170143 A) cannot be applied to a hybrid vehicle having a power split mechanism.